1. Field of the Invention
The present invention pertains to tools for use in completing oil and/or gas wells. Specifically, it pertains to a washing tool and method suitable for circulating fluid through well conduits and surrounding formations for various treatments thereof.
2. Description of the Prior Art
In completing an oil or gas well after drilling a hole therefor, it is common to install a production casing and to perforate the casing at the producing formation. After completion, the oil and/or gas flows from the formation through the perforations into the production casing where it is usually communicated to the surface of the well through production tubing.
Frequently it is necessary or desirable to treat the formation surrounding the perforated casing in some way to enhance the flow of fluids therefrom. Some methods of treating formations include circulating water or acidized fluid through the formation via the casing perforations and back up the casing string. By such circulation, loose sands may be washed from the formation or consolidated with various materials. Voids may be created for more effective gravel packing, tight formations may be made more susceptible to flow, etc.
In performing such circulating operations, various washing tools have been developed which generally provide some method of packing off an area of the casing for circulation. Such tools are usually attached to the lower end of a washing string, lowered into the casing to the desired depth, packed off and circulating commenced. In most of the tools of the prior art, packing is accomplished by providing packers on the washing tools on opposite sides of the perforations through which the fluid is to flow from the tool. Circulating fluid flows down the circulating string, through the tool, between the packers and out the casing perforations into the formation. Flow then continues back into the casing through perforations above the packers so that the returning fluid flows upwardly through the casing above the tool.
The packers used in washing tools of the prior art are usually of the cup type. Prior art washing tools utilizing cup type packers are made by the Baker Division of Baker Oil Tools, Inc. and Cavins Corporation. Cup type packers leave something to be desired in dependability, failing to adequately seal under many conditions. Furthermore, since the cup type packers engage the casing while the tool is being run into the well or pulled out of it, they are frequently torn or damaged during use.
Upon completion of circulation, it may be desirable to reverse circulate for removing sand or other materials from the bottom of the well hole. This is difficult to effectively accomplish with cup type packers since the packers remain engaged with the casing and since some of them may be flared in a direction which would actually oppose reverse flow. Another problem associated with cup type packers is the possibility of swabbing in the well or pulling sand into the casing when the tool is removed therefrom.